1. Field of the Invention
This invention relates to interlocks for switchgear, and particularly to apparatus which permits tripping and discharge of the springs from the top of the unit.
2. Background Information
Medium voltage switchgear typically comprise a switching mechanism housed in a metal enclosure. The switching mechanism incudes separable contacts for each phase and a common spring operated closing and tripping device. This device includes a spring which trips the contacts open and a pair of closing springs which close the contacts and charge the opening spring. The closing springs are charged manually by a lever arm through a ratchet coupling, and alternatively in some installations, by an electric motor.
The separable contacts are closed by releasing the energy stored in the closing springs through activation of a closing trigger mechanism. This can be done manually or remotely through a solenoid. An electronic trip circuit monitors the load currents and actuates an opening trigger mechanism through an opening solenoid if the current exceeds certain current-time characteristics.
In one type of such medium voltage switchgear, the switching mechanism is mounted in a drawer which rolls on horizontal rails into engagement with line and load conductor terminations within the enclosure. In another arrangement, the switching mechanism is moved horizontally into the enclosure and then raised vertically for engagement with the terminations.
The forces required for rapid opening of the separable contacts of the circuit breaker dictate the use of a sizable opening spring. The combined forces generated by the closing springs is even larger, as they charge the opening springs, as well as close the separable contacts.
The energy stored in these springs creates a potential danger to service personnel which is in addition to the electrical hazard. It is important then that all of the springs are discharged before maintenance is performed on the breaker, or before it is removed from the enclosure.
The type of switchgear in which the circuit breaker moves horizontally into engagement with the conductor terminations includes a cam mechanism below the circuit breaker which actuates the trip mechanisms to automatically discharge both the closing and opening springs as the circuit breaker is inserted or removed from the cabinet. The other type of switchgear in which the circuit breaker is raised to engage the conductor terminations does not have a mechanism which can trip the spring release triggers from below the circuit breaker. Instead, the circuit breakers in this type of switchgear have devices actuated from above to trip the spring release triggers.
There is a need for apparatus which enables circuit breakers of the type designed for moving horizontally into engagement with the conductor terminations to be used in switchgear in which the circuit breaker is raised to engage the conductor terminations.
Specifically, there is a need for apparatus which trips the spring release triggers of such circuit breakers from above.
Furthermore, there is a need for such apparatus which requires minimal modification to the circuit breaker and which is economical and easy to install.